Semiconductor device including gate electrode extending between nanosheets

ABSTRACT

A semiconductor device according to example embodiments of inventive concepts may include a substrate, source/drain regions extending perpendicular to an upper surface of the substrate, a plurality of nanosheets on the substrate and separated from each other, and a gate electrode and a gate insulating layer on the substrate. The nanosheets define channel regions that extend in a first direction between the source/drain regions. The gate electrode surrounds the nanosheets and extends in a second direction intersecting the first direction. The gate insulating layer is between the nanosheets and the gate electrode. A length of the gate electrode in the first direction may be greater than a space between adjacent nanosheets among the nanosheets.

CROSS-REFERENCE TO RELATED APPLICATION

This U.S. Non-Provisional patent application claims priorities under 35USC §119 to Korean Patent Application No. 10-2016-0023387, filed on Feb.26, 2016, in the Korean Intellectual Property Office, the disclosures ofwhich are incorporated by herein by reference in their entirety.

BACKGROUND

The present disclosure relates to a semiconductor device.

Semiconductor devices are important elements in the electronic industry.Storage devices for storing data, processors for processing data and thelike may be provided by semiconductor devices. Recently, a number ofstudies aimed at improving a degree of integration of semiconductordevices and reducing the power consumption thereof have been undertaken.In addition, various studies aimed at developing a semiconductor devicehaving a three dimensional structure, in order to reduce limitationscaused by a decrease in size of a semiconductor element included in asemiconductor device, have been carried out.

SUMMARY

The present disclosure relates to a semiconductor device that limits(and/or prevents) formation of voids between a plurality of channelregions in a fabrication process.

According to example embodiments of inventive concepts, a semiconductordevice may include a substrate, source/drain regions on the substrate, aplurality of nanosheets on the substrate between the source/drainregions, a gate electrode on the substrate and surrounding the pluralityof nanosheets, and a gate insulating layer on the substrate between theplurality of nanosheets and the gate electrode. The source/drain regionsextend perpendicular to an upper surface of the substrate. The pluralityof nanosheets are separated from each other. The plurality of nanosheetsdefine channel regions that extended in a first direction. The gateelectrode extends in a second direction that intersects the firstdirection. A length of the gate electrode in the first direction may begreater than a space between adjacent nanosheets among the plurality ofnanosheets.

According to example embodiments of inventive concepts, a semiconductordevice may include a substrate, a plurality of nanosheets on thesubstrate and extending in a first direction, and a gate electrode onthe substrate burying the plurality of nanosheets. The gate electrodeincludes a first region between the plurality of nanosheets and a secondregion surrounding the first region. The first region and the secondregion have different stack structures from each other.

According to example embodiments of inventive concepts, a semiconductordevice may include a substrate, source/drain regions on the substrate, aplurality of nanosheets on the substrate, a gate insulating layer on thesubstrate surrounding the plurality of nanosheets, and a gate electrodeon the substrate and burying the plurality of nanosheets. Thesource/drain regions extend perpendicular to an upper surface of thesubstrate. The plurality of nanosheets extended a first direction overthe upper surface of the substrate and connect to the source/drainregions. The plurality of nanosheets are separated from each other inthe direction perpendicular to the upper surface of the substrate. Thegate electrode includes a first region between the plurality ofnanosheets and a second region surrounding the first region. The numberof metal layers included in the first region is less than the number ofmetal layers included in the second region. A length of the gateelectrode is greater than or equal to about 1.2 times a space betweenadjacent nanosheets among the plurality of nanosheets.

According to example embodiments of inventive concepts, a semiconductordevice includes a pair of source/drain regions spaced apart from eachother in a first direction, a plurality of nanosheets between the pairof source drain regions, a gate electrode, and a gate insulating layer.The pair of source/drain regions include sidewalls that face each other.The plurality of nanosheets are spaced apart from each other along thesidewalls of the pair of source/drain regions. The plurality ofnanosheets include a semiconductor material. The gate electrode includesa first region extending between the plurality of nanosheets and asecond region on an uppermost one of the plurality of nanosheets. Thefirst region is connected to the second region. The gate insulatinglayer is between gate electrode and the plurality of nanosheets. Thegate insulating layer extends between the gate electrode and the pair ofsource/drain regions.

BRIEF DESCRIPTION OF DRAWINGS

The above and other aspects and features of inventive concept will bemore clearly understood from the following detailed description taken inconjunction with the accompanying drawings, in which:

FIG. 1 is a schematic plan view of a semiconductor device according toexample embodiments of inventive concepts;

FIG. 2 is a perspective view of a portion of a semiconductor deviceaccording to example embodiments of inventive concepts;

FIG. 3 is a cross-sectional view taken along line of the semiconductordevice illustrated in FIG. 2;

FIG. 4 is an enlarged view of region A of the semiconductor deviceillustrated in FIG. 3;

FIG. 5 is a cross-sectional view taken along line V-V′ of thesemiconductor device illustrated in FIG. 2;

FIG. 6 is a cross-sectional view taken along line VI-VI′ of thesemiconductor device illustrated in FIG. 2;

FIG. 7 is a perspective view of a portion of a semiconductor deviceaccording to example embodiments of inventive concepts;

FIG. 8 is a cross-sectional view taken along line VIII-VIII′ of thesemiconductor device illustrated in FIG. 7;

FIG. 9 is an enlarged view of region B of the semiconductor deviceillustrated in FIG. 8;

FIG. 10 is a cross-sectional view taken along line X-X′ of thesemiconductor device illustrated in FIG. 7;

FIG. 11 is a cross-sectional view taken along line XI-XI′ of thesemiconductor device illustrated in FIG. 7;

FIGS. 12 to 53 are drawings illustrating a method for fabricating thesemiconductor device illustrated in FIG. 2;

FIGS. 54 to 65 are drawings illustrating a method for fabricating thesemiconductor device illustrated in FIG. 7; and

FIGS. 66 and 67 are block diagrams of electronic devices includingsemiconductor devices according to example embodiments of inventiveconcepts.

DETAILED DESCRIPTION

Hereinafter, example embodiments of inventive concepts will be describedas follows with reference to the attached drawings.

FIG. 1 is a schematic plan view of a semiconductor device according toexample embodiments of inventive concepts.

Referring to FIG. 1, a semiconductor device 10 according to exampleembodiments of inventive concepts may include a plurality of finstructures F provided as an active area and a plurality of gateelectrodes 130 formed to intersect the fin structures F. The pluralityof fin structures F may be formed in a direction perpendicular to anupper surface (X-Y plane in FIG. 1) of a substrate. The substrate mayinclude a semiconductor material. The plurality of fin structures F mayinclude source/drain regions doped with impurities, and a channel regionmay be formed between the source/drain regions.

The channel region may be buried in the gate electrode 130. For example,the gate electrode 130 may be formed to surround the channel region andto intersect the plurality of fin structures F. The channel region maybe provided by a nanosheet disposed between the source/drain regions. Inexample embodiments, the nanosheet may have a thickness in the range ofseveral to several tens of nanometers (e.g., 2 nm to 100 nm).

The gate electrode 130 may be formed of a conductive material, such asmetal, metal silicide, polysilicon, or the like, and combinationsthereof. The gate electrode 130 may include a plurality of layers. Whenthe gate electrode 130 includes the plurality of layers, the gateelectrode 130 may include a work function metal layer, a barrier metallayer, a gate metal layer and the like. In example embodiments, aprotection layer 150, which limits (and/or prevents) oxygen frompermeating into the gate electrode 130, may be provided on an upperportion of the gate electrode 130.

A gate insulating layer 110 and a spacer 140 may be disposed on sides ofthe gate electrode 130. In a similar manner to the gate electrode 130,the gate insulating layer 110 and the spacer 140 may be formed tosurround the channel region CH and to intersect the plurality of finstructures F. The gate electrode 130 may extend in one direction (e.g.,direction of a Y-axis in FIG. 1) while being in contact with the finstructure F.

The gate insulating layer 110 may include a plurality of layers. Inexample embodiments, the gate insulating layer 110 may include a firstinsulating layer 111 and a second insulating layer 112. The first andsecond insulating layers 111 and 112 may have different permittivities.For example, when the first insulating layer 111 is disposed closer tothe channel region CH than the second insulating layer 112 disposedthereto, the first insulating layer 111 may have a lower permittivitythan that of the second insulating layer 112.

FIG. 2 is a perspective view of a portion of a semiconductor deviceaccording to example embodiments of inventive concepts.

Referring to FIG. 2, a semiconductor device 100 according to exampleembodiments may include a substrate 101, source/drain regions 104 and105 formed on the substrate 101, and a gate electrode 130 formed tointersect source/drain regions 104 and 105. The gate electrode 130 maybe formed to surround a channel region disposed between the source/drainregions 104 and 105. In addition, a gate insulating layer 110 and aspacer 140 may be disposed on sides of the gate electrode 130. The gateinsulating layer 110 may be also disposed between the gate electrode 130and the channel region CH.

The channel regions may be provided by a plurality of nanosheets. Theplurality of nanosheets may be disposed between the source/drain regions104 and 105. The plurality of nanosheets may be separated from eachother in a direction (direction of a Z-axis in FIG. 2) perpendicular toan upper surface of the substrate 101. Spaces between the plurality ofnanosheets may be filled with the gate electrode 130.

A substrate insulating layer 103 may be provided on the substrate 101,and disposed to surround a portion of the substrate 101. In exampleembodiments, a portion of the substrate 101 may protrude upwardly to beconnected to the source/drain regions 104 and 105. The substrateinsulating layer 103 may be disposed to surround sides of the protrudingportion of the substrate 101. An upper surface of the substrateinsulating layer 103 may be coplanar with that of the substrate 101. Inaddition, an interlayer insulating layer may be disposed on thesubstrate insulating layer 103 to cover the gate electrode 130 and thesource/drain regions 104 and 105.

FIG. 3 is a cross-sectional view taken along line of the semiconductordevice illustrated in FIG. 2. FIG. 4 is an enlarged view of region A ofthe semiconductor device illustrated in FIG. 3.

Referring to FIG. 3, the semiconductor device 100 may include aplurality of nanosheets 121 to 124 (nanosheets 120) separated from eachother along one direction (direction of a Z-axis in FIG. 3) on thesubstrate 101, the source/drain regions 104 and 105 connected to eachother by the nanosheets 120, the gate electrode 130 and the like. Thegate electrode 130 may be formed to bury the plurality of nanosheets120. The gate insulating layer 110 may be disposed between the gateelectrode 130 and the plurality of nanosheets 120. The number and adisposition of the nanosheets 120 are not limited to the configurationof FIG. 3, and may be variously changed.

The plurality of nanosheets 120 may provide the channel regions CH. Thechannel regions CH may be provided by portions of the nanosheets 120adjacent to the gate insulating layer 110 and the gate electrode 130.When a voltage more than threshold voltage of the semiconductor device100 is applied to the gate electrode 130, a depletion region may beformed on the channel regions CH to flow a current between thesource/drain regions 104 and 105. The threshold voltage may bedetermined by a material contained in the gate electrode 130 and a stackstructure of the gate electrode 130.

In example embodiments, the gate electrode 130 may include the workfunction metal layer 132 and 133, and the gate metal layer 134. Thebarrier metal layer 131 may be further provided between the workfunction metal layer 132 and 133, and the gate insulating layer 110. Thebarrier metal layer 131 may be formed of tantalum nitride (TaN),tantalum nitride oxide (TaNO), tantalum silicon nitride (TaSiN),titanium silicon nitride (TiSiN) and the like. The stack structure ofthe gate electrode 130 is not limited to the configuration of FIG. 3,and may be variously changed.

The work function metal layer 132 and 133 may determine a thresholdvoltage of the semiconductor device 100. In example embodiments, thework function metal layer 132 and 133 may include a first work functionmetal layer 132 and a second work function metal layer 133 stacked oneach other. The first and second work function metal layers 132 and 133may include different materials from each other. A material of the workfunction metal layer 132 and 133 may vary depending on whether thesemiconductor device 100 is an n-type semiconductor device or a p-typesemiconductor device. When the semiconductor device 100 is the n-typesemiconductor device, the work function metal layer 132 and 133 mayinclude hafnium, zirconium, titanium, tantalum, aluminum and metalcarbide including the above-described metal. When the semiconductordevice 100 is the p-type semiconductor device, the work function metallayer 132 and 133 may include ruthenium, palladium, platinum, cobalt,nickel and oxides thereof. However, the materials of the work functionmetal layer 132 and 133 may be variously modified in addition to theabove materials.

The gate metal layer 134 may be filled a space defined on the workfunction metal layer 132 and 133. An upper surface of the gate metallayer 134 may be coplanar with that of the second work function metallayer 133. The gate metal layer 134 may be formed of titanium nitride(TiN).

Referring to FIG. 3, in the semiconductor device 100 according toexample embodiments, a gate length Lg may be greater than a spacingT_(N) between adjacent ones of the nanosheets 120. The gate length Lgmay be defined as a length of the gate electrode 130 or a spacingbetween the spacers in a first direction (direction of an X-axis in FIG.3). In example embodiments, a gate length Lg may be greater than orequal to about 1.2 times the spacing T_(N) between the nanosheets 120. Athickness (thickness of the Z-axis direction) of the nanosheet 120 maybe less than or equal to about 50 nm, and the length (length of theX-axis direction) of the nanosheet 120 may be several tens of nanometers(e.g., 2 nm to 100 nm). The nanosheet 120 may have the length greaterthan the thickness thereof. The nanosheet 120 may also have thethickness less than or equal to the spacing T_(N) therebetween. Inexample embodiments, the spacing T_(N) between the nanosheets 120 may begreater than 0 nm and less than or equal to about 30 nm.

When the thickness of the nanosheet 120 is less than or equal to about0.8 times the spacing T_(N) between the nanosheets 120, a space betweenthe nanosheets 120 may be filled with the gate insulating layer 110 andthe gate electrode 130 without lowering a degree of integration of thesemiconductor device 100. In addition, a sum of the spacing T_(N)between adjacent ones of the nanosheets 120 and the thickness of thenanosheet 120 may be substantially the same as the gate length Lg of thegate electrode 130.

A thickness of the spacer 140 (thickness of the X-axis direction) may bearound 10 nm (e.g., in a range of about 5 nm to about 15 nm), and thegate length Lg of the gate electrode 130 may be determined bysubtracting twice the thickness of the spacer 140 from the length of thenanosheet 120. As previously described, the gate length Lg of the gateelectrode 130 may be determined to a value greater than or equal toabout 1.2 times the spacing T_(N) between the nanosheets 120.Accordingly, in example embodiments, a thickness of the spacer 140, alength of the nanosheet 120 and a spacing T_(N) between the nanosheets120 may be determined according to conditions such as Equation 1 below.1.2*T _(N)≦(a length of a nanosheet−thickness of a spacer)  [Equation 1]

In order to limit (and/or prevent) a space between the nanosheets 120from being incompletely filled with the gate electrode 130, the gateelectrode 130 may be formed to have the gate length Lg greater than thespacing T_(N) between the nanosheets 120. The gate electrode 130 may beformed by removing a dummy gate provided between the spacers 140 andthen filling a space from which the dummy gate has been removed, with ametal material. Before filling the space with the metal material, thegate insulating layer may be formed first on an inner side of the spacer140 and an outer side of the nanosheet 120. In this case, if the spacebetween the spacers 140 is first filled with the metal material beforefilling the space between the nanosheets 120, the space between thenanosheet 120 may be incompletely filled with the metal material.Accordingly, voids may be generated from the incompletely filled space.Accordingly, a performance of the semiconductor device 100 may bedeteriorated due to the void in the space between nanosheets 120.

Accordingly, in order to limit and/or prevent a void in the spacebetween the nanosheets, the gate electrode 130 may be formed so as tohave the larger length Lg than the spacing T_(N) between the nanosheets120. In addition, the gate length Lg may correspond to the spacingbetween the spacers 140. Accordingly, by securing a sufficient spacebetween the spacers 140, the space between the nanosheets 120 may befirst filled with the gate electrode 130 before filling the spacebetween the spacers 140 with the gate electrode 130.

Referring to FIG. 4, the gate insulating layer 110 may include aplurality layers. In example embodiments, the gate insulating layer 110may include a first insulating layer and a second insulating layer. Thefirst and second insulating layers 111 and 112 may have differentpermittivities from each other. The permittivity of the secondinsulating layer may be greater than that of the first insulating layer.In this case, the second insulating layer may be disposed closer to thegate electrode 130 than the first insulating layer disposed thereto. Inother words, the first insulating layer may be disposed closer to thechannel region CH than the second insulating layer disposed thereto. Bydisposing the first insulating layer having a relatively low level ofpermittivity to be closer to the channel region CH than the secondinsulating layer having a relatively high level of permittivity,characteristics of the memory device such as erase characteristics maybe improved. Meanwhile, the second insulating layer having a relativelyhigh level of permittivity may be thicker than the first insulatinglayer.

The second insulating layer 112 having a relatively high level ofpermittivity may include silicon oxide (SiO₂), silicon nitride (Si₃N₄),silicon oxynitride (SiON), or a high dielectric constant material. Ahigh dielectric constant material may be a material, such as aluminiumoxide (Al₂O₃), tantalum oxide (Ta₂O₃), titanium oxide (TiO₂), yttriumoxide (Y₂O₃), zirconium oxide (ZrO₂), zirconium silicon oxide(ZrSi_(x)O_(y)), hafnium oxide (HfO₂), hafnium silicon oxide(HfSi_(x)O_(y)), lanthanum oxide (La₂O₃), lanthanum aluminium oxide(LaAl_(x)O_(y)), lanthanum hafnium oxide (LaHf_(x)O_(y)), hafniumaluminium oxide (HfAl_(x)O_(y)), and praseodymium oxide (Pr₂O₃).

In addition, only the barrier metal layer 131 and the work functionmetal layer 132 and 133 among the plurality of metal layers 131 to 134may be disposed between adjacent ones of the nanosheets 120. In FIG. 4,a space between adjacent ones of nanosheets may be filled with thebarrier metal layer 131 and the first work function metal layer 132only. The number of metal layers 131 to 134 disposed between thenanosheets 120 may be determined by the spacing T_(N) between thenanosheets 120 and each thickness of metal layers 131 to 134.

FIG. 5 is a cross-sectional view taken along line V-V′ of thesemiconductor device illustrated in FIG. 2.

Referring to FIG. 5, the plurality of nanosheets 120 may be disposed onthe substrate 101. The plurality of nanosheets 120 may include first tofourth nanosheets 121 to 124. The fourth nanosheet 124 may be on anupper surface of the substrate 101, and the first to third nanosheets121 to 123 may be separated from the substrate 101. The first to fourthnanosheets 121 to 124 may be separated from each other to dispose thegate insulating layer 110 and a portion of the gate electrode 130 eachbetween adjacent ones of the nanosheets 120. In other words, at least aportion of the first to fourth nanosheets 121 to 124 may be buried bythe gate electrode 130.

The gate electrode 130 may include the barrier metal layer 131, the workfunction metal layer 132 and 133, and the gate metal layer 134. Theplurality of metal layers 131 to 134 included in the gate electrode 130may be sequentially stacked on each of the nanosheets 120. In FIG. 5, aspace between adjacent ones of the nanosheets 120 may be filled with thebarrier metal layer 131 and the first work function metal layer 132only.

In other words, when the gate electrode 130 is divided into a firstregion disposed between adjacent ones of the nanosheets 120 and a secondregion other than the first region, the first region may not include thesecond work function metal layer 133 and the gate metal layer 134.According, the first region disposed between adjacent ones of thenanosheets 120 may have a different stack structure from that of thesecond region. In example embodiments, the number of metal layersincluded in the first region may be less than the number of metal layersincluded in the second region. Meanwhile, the second region may bedefined as a region which surrounds the first region.

FIG. 6 is a cross-sectional view taken along line VI-VI′ of thesemiconductor device illustrated in FIG. 2.

Referring to FIG. 6, in a cross-section taken along line VI-VI′, thegate electrode 130 is not illustrated, and a structure of the pluralityof nanosheets 120 surrounded by the spacers 140 may be illustrated. Inexample embodiments, the first to third nanosheets 121 to 123 may besurrounded by the spacers 140 in Y-axis and Z-axis directions.

At least portions of the plurality of nanosheets 120 may pass throughthe spacers 140 to be connected the source/drain regions 104 and 105.Referring to FIG. 3 along with FIG. 6, both sides of each of the firstto third nanosheets 121 to 123 may be connected to the source/drainregions 104 and 105, may be surrounded by the gate electrode 130 and thespacers 140.

FIG. 7 is a perspective view of a portion of a semiconductor deviceaccording to example embodiments of inventive concepts.

Referring to FIG. 7, according to example embodiments of inventiveconcepts, a semiconductor device 200 may include a substrate 201,source/drain regions 204 and 205 formed on the substrate 201, a gateelectrode 230 formed to intersect the source/drain regions 204 and 205,and the like. In a similar manner to that of the semiconductor device100 in FIG. 2, a gate insulating layer 210 and spacers 240 may be formedon sides of the gate electrode 230, and a portion of the substrate 201may protrude upwardly to be connected the source/drain regions 204 and205. The protruding portion of the substrate 201 may be surrounded by asubstrate insulating layer 203.

In the semiconductor device 200 in FIG. 7, the gate electrode 230 mayinclude a work function metal layer 231 and 232 and a gate metal layer233. In the semiconductor device 100 in FIG. 2, the barrier metal layer131 may be included in the gate electrode 130, while a barrier metallayer may not present in the semiconductor device 200 in FIG. 7.Accordingly, a thickness of the work function metal layer 231 and 232may be different from that a thickness of the work function metal layerof the example embodiment illustrated in FIG. 2. Due to a difference inphysical properties of the gate electrodes, each of the semiconductordevices 100 and 200 illustrated in FIGS. 2 and 7 may have differentthreshold voltages from each other.

FIG. 8 is a cross-sectional view taken along line VIII-VIII′ of thesemiconductor device illustrated in FIG. 7. FIG. 9 is an enlarged viewof region B of the semiconductor device illustrated in FIG. 8.

Referring to FIG. 8, in the semiconductor device 200 according toexample embodiments of inventive concepts, a spacing T_(N) betweenadjacent ones of a plurality of nanosheets 220 may be smaller than agate length Lg of the gate electrode 230.

As described with reference to FIG. 3, the gate length Lg may be definedas a length of the gate electrode 230 in one direction (direction of anX-axis in FIG. 8), and may correspond to a spacing between the spacers240. By defining the relationship between the gate length Lg and thespacing T_(N) between the nanosheets 220, as described above, it may belimited (and/or prevented) from incompletely filling the space betweenthe nanosheets with the gate electrode 230.

Referring to FIG. 9, a gate insulating layer 210 may include a firstinsulating layer 211 and a second insulating layer 212. As describedwith reference to FIG. 4, the first and second insulating layers 211 and212 may have different permittivities from each other. The permittivityof the second insulating layer 212 may be greater than that of the firstinsulating layer 211.

In addition, a space between adjacent ones of the nanosheets 220 may befilled with the gate insulating layer 210 and the first work functionmetal layer 231 only. The spacing T_(N) between adjacent ones of thenanosheets 210 may be smaller than about 2 times a sum of thickness ofthe gate insulating layer 210 and thickness of the first work functionmetal layer 231.

FIG. 10 is a cross-sectional view taken along line X-X′ of thesemiconductor device illustrated in FIG. 7. FIG. 11 is a cross-sectionalview taken along line XI-XI′ of the semiconductor device illustrated inFIG. 7.

Referring to FIG. 10, the plurality of nanosheets 220 may be surroundedby the gate insulating layer 210 and the gate electrode 230. The gateelectrode 230 may include the work function metal layer 231 and 232, andthe gate metal layer 233. The work function metal layer 231 and 232 mayinclude the first and second work function metal layers 231 and 232, andthe first and second work function metal layers 231 and 232 may havedifferent metal materials from each other.

Referring to FIG. 11, the plurality of the nanosheets 220 may besurrounded by the gate electrode 230 and the spacers 240 disposedbetween the source/drain regions 204 and 205. At least portions of theplurality of the nanosheets 220 may pass through the spacers 240 to berespectively connected to the source/drain regions 204 and 205.

In FIGS. 8 to 10, the space defined between the plurality of nanosheets220 may be filled with the gate insulating layer 210 and the first workfunction metal layer 231. In other words, the gate insulating layer 210and the first work function metal layer 231 may be disposed betweenadjacent ones of the plurality of nanosheets 220. The gate electrode 230may be divided into a first region disposed between adjacent ones of thenanosheets 220 and a second region other than the first region. The gateelectrode 230 may include different stack structures according to thefirst region and the second region. In the first region, the gateelectrode 230 may be a stack structure including only the first workfunction metal layer 231. In the second region, the gate electrode 230may be a stack structure including the first and second work functionmetal layer 231 and 232, and the gate metal layer 233.

FIGS. 12 to 53 are drawings illustrating a method for fabricating thesemiconductor device illustrated in FIG. 2. FIG. 14 is a cross-sectionalview taken along lines XIV-XIV′ of FIG. 13. FIGS. 17 and 18 arecross-sectional views taken along lines XVII-XVII′ and XVII-XVIII′ ofFIG. 16. FIGS. 21 to 23 are cross-sectional views taken along linesXXI-XXI′, XXII-XXII′ and XXIII-XXIII′ of FIG. 20. FIG. 26 is across-sectional view taken along line XXVI-XXVI′ of FIG. 25. FIG. 29 isa cross-sectional view taken along line XXIX-XXIX′ of FIG. 28. FIG. 32is a cross-sectional view taken along line XXXII-XXXII′ of FIG. 31. FIG.35 is a cross-sectional view taken along line XXXV-XXXV′ of FIG. 34.FIG. 38 is a cross-sectional view taken along line XXXVIII-XXXVIII′ ofFIG. 37. FIG. 41 is a cross-sectional view taken along line XLI-XLI′ ofFIG. 41. FIG. 44 is a cross-sectional view taken along line XLIV-XLIV′of FIG. 43. FIG. 47 is a cross-sectional view taken along lineXLVII-XLVII′ of FIG. 46. FIG. 50 is a cross-sectional view taken alongline L-L′ of FIG. 49. FIG. 53 is a cross-sectional view taken along lineLIII-LIII′ of FIG. 52.

Referring to FIGS. 12 to 14, a plurality of semiconductor layers 121S to124S (semiconductor layers 120S) and a plurality of sacrificial layers161S to 163S (sacrificial layers 160S) may be alternately stacked on asubstrate 101. FIG. 13 illustrates a top plan view of the perspectiveview shown in FIG. 12 as it may be viewed through the X-Y plane. Theplurality of semiconductor layers 120S may include a semiconductormaterial, and the plurality of sacrificial layers 160S may include amaterial having a etch selectivity with respect to the plurality ofsemiconductor layers 120S. In example embodiments, the plurality ofsemiconductor layers 120S may include silicon (Si), and the plurality ofsacrificial layers 160S may include silicon germanium (Site).

Respective thicknesses of the plurality of semiconductor layers 120S andsacrificial layers 160S may be variously changed according to exampleembodiments. In example embodiments, thicknesses of plurality ofsemiconductor layers 120S may be less than those of the plurality ofsacrificial layers 160S. The plurality of sacrificial layers 160S may beremoved in subsequent process, and replaced with a gate insulating layer110 and a gate electrode 130. Accordingly, thicknesses of the pluralityof sacrificial layers 160S may be substantially equal to spacingdistances between the plurality of nanosheets 120, respectively.

Referring to FIGS. 15 to 18, a fin structure F may be formed by removingportions of the plurality of semiconductor layers 120S and sacrificiallayers 160S. FIG. 16 illustrates a top plan view of the perspective viewshown in FIG. 15 as it may be viewed through the X-Y plane. Referring toFIGS. 15 to 18 together, the fin structure F may include the pluralityof semiconductor layers 121F to 124F (semiconductor layers 120F) andsacrificial layers 161F to 163F (sacrificial layers 160F) alternativelystacked on the substrate 101.

In order to form the fin structure F, at least a portion of thesubstrate 101 may be removed from an upper surface thereof, and thesubstrate insulating layer 103 may be disposed therein. In this case, anupper surface of the substrate insulating layer 103 may be coplanar withthe uppermost surface of the substrate 101.

As illustrated in FIG. 1, the fin structure F may extend on thesubstrate 101 in a specific direction, for example, in a direction ofthe X-axis of FIG. 1. The fin structures F may be disposed at desired(and/or alternatively predetermined) intervals therebetween. In exampleembodiments, a respective width of and an interval between the finstructures F in a direction of the Y-axis may be several tens ofnanometers (e.g., 20 nm to 100 nm). A thickness of each of the pluralityof semiconductor layers 120F may be in the range of three to thirty ofnanometers. A thickness of each of the plurality of sacrificial layers160F may be greater than that of each of the plurality of semiconductorlayers 120F.

Referring to FIGS. 19 to 23, a dummy gate 130 a and first spacers 140 amay be formed on the fin structure F. FIG. 20 illustrates a top planview of the perspective view shown in FIG. 19 as it may be viewedthrough the X-Y plane. In example embodiments, a capping layer may befurther formed on the dummy gate 130 a, and a etch stop layer may befurther formed between the dummy gate 130 a and the plurality ofsemiconductor layer 120F.

The dummy gate 130 a and the first spacers 140 a may be formed in a formin which they are in contact with the fin structure F. The dummy gate130 a may be formed of polysilicon, or the like, and the first spacers140 a may be formed using an insulating material such as silicon oxide,silicon nitride, and the like.

The dummy gate 130 a may be replaced with a gate electrode 130 in asubsequent process. Accordingly, a gate length Lg of the gate electrode130 may be substantially equal to a width of the dummy gate 130 a in onedirection (direction of a Y-axis in FIGS. 19 to 23). In exampleembodiments, the width of the dummy gate 130 a may be greater than athickness of each of the plurality of sacrificial layers 160F.Accordingly, in a subsequent process for forming the gate electrode 130after removing the dummy gate 130 a, a space in which sacrificial layers160F are removed, may be filled with the gate electrode 130 withoutvoids.

In example embodiments, the width of the dummy gate 130 a may bedetermined by greater than or equal to about 1.2 times the value of eachthickness of the plurality of sacrificial layers 160F. In addition, thewidth of the dummy gate 130 a may be substantially the same as a sum ofeach thickness of the plurality of semiconductor layers 120F and eachthickness of the plurality of sacrificial layers 160F.

Referring to FIGS. 24 TO 26, by performing an etching process using thedummy gate 130 a and the first spacers 140 a as an etch mask, at least aportion of the fin structure F may be removed to form a plurality ofnanosheets 121 to 124 (nanosheets 120). Each of the plurality ofnanosheets 120 may be surrounded by the dummy gate 130 a and the firstspacers 140 a. The plurality of sacrificial layers 161 to 163(sacrificial layers 160) may be disposed between the plurality ofnanosheets 120.

As illustrated in FIGS. 24 to 26, a portion of an upper surface of thesubstrate 101 may be exposed externally from the dummy gate 130 a andthe first spacers 140 a. The upper surface of the substrate 101 may beused to form source/drain regions 104 and 105 using an epitaxialprocess.

Referring to FIGS. 27 to 29, portions of the sacrificial layers 160exposed on the sides of the dummy gate 130 a and the first spacers 140 amay be removed to form a spacer space S. As illustrated FIGS. 27 to 29,at least portions of the first to third sacrificial layers 161 to 163may be removed to form the spacer space S. In this case, a depth of thespacer space S may be substantially equal to a thickness of the firstspacer 140 a.

Referring to FIGS. 30 to 32, second spacers 140 b may be formed byfilling the spacer spaces S with an insulating material. A thickness ofthe second spacers 140 b may be substantially equal to that of the firstspacers 140 a. An outer surface of the second spacer 140 b may becoplanar with an outer surface of the first spacer 140 a. The firstspacers 140 a and the second spacers 140 b may be provided as thespacers 140 surrounding a gate electrode that will be sequentiallyformed. The second spacer 140 b may be formed of the same material asthat of the first spacer 140 a. In example embodiments, the firstspacers 140 a and the second spacers 140 b may include silicon oxide,silicon nitride, or the like.

Referring to FIGS. 33 to 35, source/drain regions 104 and 105 may beformed from the upper surface of the substrate 101 using a selectiveepitaxial growth (SEG). The source/drain regions 104 and 105 may includea semiconductor material doped with a desired (and/or alternativelypredetermined) impurity. A thickness of the source/drain regions 104 and105 may be variously changed. Upper surfaces of the source/drain regions104 and 105 may be coplanar with an upper surface of the nanosheet 121disposed on an uppermost level of the nanosheets 120.

Referring to FIGS. 36 to 38, an interlayer insulating layer 170 may beformed on the substrate 101. The interlayer insulating layer 170 may beformed to cover outer sides of the spacers 140 and the source/drainregions 104 and 105.

Referring to FIGS. 39 to 41, the dummy gate 130 a may be removed. Thedummy gate 130 a may be selectively removed based on an etchingselectivity of the dummy gate 130 a with respect to the first spacers140 a and the source/drain regions 104 and 105. The nanosheets 121 to124 and the sacrificial layers 161 to 163 may be exposed externally froma space between the first spacers 140 a by removing the dummy gate 130a.

Referring to FIGS. 42 to 45, the sacrificial layers 160 may beselectively removed to form horizontal openings H. As described above,the sacrificial layer 160 may include a different material from thenanosheets 120, such as a material having a desired (and/oralternatively predetermined) etching selectivity with respect to amaterial included in the nanosheets 120. In example embodiments, thenanosheets 120 may include a semiconductor material, such as silicon, toprovide a channel region of the semiconductor device 100, and thesacrificial layers 160 may include silicon germanium. In order toselectively remove exposed portions of the sacrificial layers 160 whilesuppressing the etching of the nanosheets 120, an etchant having asignificant etching selectivity of silicon germanium (SiGe) with respectto silicon (Si) may be used. For example, an etchant including hydrogenperoxide (H₂O₂), hydrofluoric acid (HF), and acetic acid (CH₃COOH), anetchant including ammonium hydroxide (NH₄OH), hydrogen peroxide (H₂O₂),and deionized water (H₂O), and an etchant including peracetic acid, or acombination thereof may be used.

When the sacrificial layers 160 are removed, the nanosheets 120 may beseparated from each other. Referring to FIG. 44, the nanosheets 120 maybe separated from each other in a direction of the Z-axis, and a spacingT_(N) between the nanosheets 120 may be less than a spacing W_(D)between the first spacers 140 a. In example embodiments, the spacingW_(D) between the first spacers 140 a may be greater than or equal toabout 1.2 times the spacing T_(N) between the nanosheets 120.Accordingly, in a subsequent process for forming agate insulating layer110 and a gate electrode 130, the horizontal openings H may be firstfilled with the gate insulating layer 110 and the gate electrode 130before filling the space between the first spacers 140 a with them.Accordingly, it may be limited (and/or prevented) that voids may begenerated from the incompletely filled horizontal openings H.

Referring to FIGS. 45 to 47, a gate insulating layer may be formed. Thegate insulating layer 110 may be disposed on inner surfaces of the firstspacers 140 a and the horizontal openings H between the nanosheets 120.In example embodiments, the gate insulating layer 110 may be disposed tosurround the nanosheets 120 in directions of the Y- and Z-axes, and thehorizontal openings H may not be completely filled with the gateinsulating layer 110. In other words, after forming the gate insulatinglayer 110, there may still exist spaces between the nanosheets 120.

The gate insulating layer 110 may include a first insulating layer and asecond insulating layer which have different permittivities from eachother. The permittivity of the second insulating layer may be greaterthan that of the first insulating layer. The first insulating layer maybe disposed closer to the first spacer 140 a and nanosheet 120 than thesecond insulating layer. In other words, the first insulating layer maybe formed before forming the second insulating layer.

The gate insulating layer 110 may be formed through a process such asatomic layer deposition (ALD), chemical vapor deposition (CVD), or thelike. In example embodiments, the second insulating layer may be formedthicker than the first insulating layer. For example, a thickness of thefirst insulating layer may be less than about 1 nm, and a thickness ofthe second insulating layer may be about 1 nm to about 2 nm.

Referring to FIGS. 48 to 50, a barrier metal layer 131 and a first workfunction metal layer 132 may be sequentially formed on the gateinsulating layer 110. The space between the nanosheets 120 may beentirely filled with the barrier metal layer 131 and the first workfunction metal layer 132. Accordingly, as illustrated FIGS. 48 to 50,only the first work function metal layer 132 may be exposed externallyfrom the nanosheets 120.

Referring to FIG. 50, the space between the nanosheets 120 may becompletely filled with the gate insulating layer 110, the barrier metallayer 131 and the first work function metal layer 132. Meanwhile,referring to FIG. 48, a space where nanosheets 120 are not disposedbetween the first spacers 140 a may be not completely filled with thegate insulating layer 110, the barrier metal layer 131 and the firstwork function metal layer 132. In other words, it may be limited (and/orprevented) from generating voids from the incompletely filled spacebecause the space between the nanosheets 120 is filled first.

Referring to FIGS. 51 to 53, the second work function metal layer 133and the gate metal layer 134 may be formed on the first work functionmetal layer 132. The second work function metal layer 133 may include amaterial different from the first work function metal layer 132. Athreshold voltage of the semiconductor device 100 may be determined by amaterial and a thickness of each of the work function metal layers 132and 133. The gate metal layer 134 may be disposed on the second workfunction metal layer 133, and a protection layer 150 may be furtherprovided on the gate metal layer 134.

The protection layer 150 may be formed of a silicon nitride layer havinga thickness in the range of several to several hundreds of angstroms(e.g., 3 Å to 800 Å). The protection layer 150 may be formed for thepurpose of limiting (and/or preventing) deterioration of a thresholdvoltage induced by permeating oxygen into the gate electrode 130. Aportion of the gate electrode 130 may be removed, and the protectionlayer 150 may be formed in the removed portion of the gate electrode.

Referring to FIG. 53, the gate electrode 130 may include a first regionG1 disposed between adjacent ones of the nanosheets 120, and a secondregion G2 other than the first region G1. Because the first region G1 isdefined as a region disposed between adjacent ones of the nanosheets120, the gate electrode in FIG. 53 may include a total of three firstregions G1.

The first and second regions G1 and G2 may have different stackstructures from each other. The first region G1 may only include thebarrier metal layer 131, the first work function metal layer 132, andthe second region may include the barrier metal layer 131, the first andsecond work function metal layer 132 and 133 and the gate metal layer134. The number of metal layers included in the first region G1 may beless than the number of metal layers included in the second region G2.The number and type of metal layers of each of the first and secondregions G1 and G2 may be variously changed.

In a process of fabricating the semiconductor device 100 according toexample embodiments of inventive concepts, as illustrated in FIGS. 19 to23, the spacing W_(D) between the first spacers 140 a may be greaterthan the thickness of each of the sacrificial layers 160F. The spacingW_(D) between the first spacers 140 a may be determined by a width ofthe dummy gate 130 a. The gate electrode 130 may be formed in a regionin which the dummy gate is removed. The gate length Lg of the gateelectrode 130 may be greater than the spacing T_(N) between thenanosheets 120. Accordingly, by forming the dummy gate 130 a having thewidth greater than the thickness of each of the sacrificial layers 160F,the space between the nanosheets 120 may be filled with the gateelectrode 130 without voids.

FIGS. 54 to 65 are drawings illustrating a method for fabricating thesemiconductor device illustrated in FIG. 7. FIG. 55 is a cross-sectionalview taken along line LVI-LVI′ of FIG. 54. FIG. 59 is a cross-sectionalview taken along line LIX-LIX′ of FIG. 58. FIG. 62 is a cross-sectionalview taken along line LXII-LXII′. FIG. 65 is a cross-sectional viewtaken along line LXV-LXV′ of FIG. 64.

Referring to FIGS. 54 to 56, a dummy gate formed on a substrate 201 maybe removed to expose a plurality of nanosheets 221 to 224 (nanosheets220) in a space between first spacers 240 a. Sacrificial layers may beselectively removed to form horizontal openings H. A spacing T_(N)between adjacent ones of the nanosheets 220 may be less than a widthW_(D) between the first spacers 240 a.

Referring to FIGS. 57 to 59, the space between the first spacers 240 aand the horizontal openings H between the nanosheets 220 may be filled agate insulating layer 210

As illustrated in FIG. 9, the gate insulating layer 210 may include afirst insulating layer 211 and a second insulating layer 212. The firstand second insulating layer 211 and 212 may have differentpermittivities from each other. Each of the nanosheets 220 may besurrounded by the gate insulating layer 210. The space between thenanosheets 120 may not be completely filled with the gate insulatinglayer 210.

Referring to FIGS. 60 to 62, a first work function metal layer 231 maybe formed on the gate insulating layer 210. The space between thenanosheets 220 may be filled with the first work function metal layer231. Accordingly, as illustrated in FIG. 60, the first work functionmetal layer 231 may be exposed externally from the nanosheets 220. Thespace between the nanosheets 220 may be completely filled with the gateinsulating layer 210 and the first work function metal layer 231 withoutvoid.

In example embodiments, a spacing T_(N) between the nanosheets 220, athickness of the gate insulating layer 210 and a thickness of the firstwork function metal layer 231 may have a relationship such as Equation 2below. According to the relationship such as Equation 2, by forming thespacing T_(N) between the nanosheets 220, the gate insulating layer 210and the first work function metal layer 231, the space between thenanosheets 220 may be completely filled with the gate insulating layer210 and the first work function metal layer 231.T _(N)≦(a thickness of a gate insulating layer+a thickness of a firstwork function metal layer)*2  [Equation 2]

Referring to FIGS. 63 to 65, a second work function metal layer 232 anda gate metal layer 233 may be formed on the first work function metallayer 231. A protection layer 250 may be formed on the gate metal layer233. The second work function metal layer 232 may include a materialdifferent from the first work function metal layer 231. A thresholdvoltage of the semiconductor device 200 may be determined by thicknessand material of each of the first and second work function metal layers231 and 232.

Referring to FIG. 65, the gate electrode 230 may include a first regionG1 and a second region G2. The first region G1 may be defined as aregion disposed between the nanosheets 220, and the second region G2 maybe other than the first region G1. The first and second regions G1 andG2 may have stack structures different from each other.

The first region G1 may only include the first work function metal layer231. On the other hand, the second region G2 may include the first andsecond work function metal layers 231 and 232 and the gate metal layer233. In other words, the first region G1 may have a simple stackstructure than the second region G2. The gate electrode 230 may have itswidth greater than its thickness in the first region G1.

In example embodiments of inventive concepts, the semiconductor devices100 and 200 may be formed on one substrate. In other words, by formingthe semiconductor devices 100 and 200 having the gate electrodes 130 and230 of different stack structures, the semiconductor devices 100 and 200having different threshold voltages may be provided in one substrate.

In example embodiments of inventive concepts, the structures of the gateelectrodes 130 and 230 according to the semiconductor devices 100 and200 may be variously modified.

For example, the number of the barrier metal layer and the work functionmetal layer included in the gate electrodes 130 and 230 may be changed,and the barrier metal layer may be disposed between the work functionmetal layer and the gate metal layer. In this way, by variouslymodifying the stack structure of each of the gate electrodes 130 and230, it is possible to fabricate the semiconductor devices 100 and 200having different threshold voltages.

FIGS. 66 and 67 are block diagrams of electronic devices includingsemiconductor devices according to example embodiments of inventiveconcepts.

Referring to FIG. 66, according to example embodiments, a storage device1000 may include a controller 1010 communicating with a host, andmemories 1020-1, 1020-2, and 1020-3 storing data. The controller 1010and the memories 1020-1, 1020-2, and 1020-3 may include thesemiconductor devices 100, 200, and 300 according to various exampleembodiments described above.

The host communicating with the controller 1010 may be variouselectronic devices equipped with the storage device 1000. For example,the host may be a smartphone, a digital camera, a desktop computer, alaptop computer, a portable media player, or the like. The controller1010 may store data in the memories 1020-1, 1020-2, and 1020-3 afterreceiving requests for data writing or reading sent by the host, or maygenerate a command (CMD) to output data from the memories 1020-1,1020-2, and 1020-3.

As illustrated in FIG. 66, one or more memories 1020-1, 1020-2, and1020-3 may be connected to the controller 1010 in parallel in thestorage device 1000. By connecting the plurality of memories 1020-1,1020-2, and 1020-3 to the controller 1010 in parallel, the storagedevice 1000 having a large capacity, such as a solid state drive (SSD)may be implemented.

Referring to FIG. 67, according to example embodiments, an electronicdevice 2000 may include a communications unit 2010, an input unit 2020,an output unit 2030, a memory 2040, and a processor 2050.

The communications unit 2010 may include a wired/wireless communicationsmodule, for example, a wireless Internet module, a near fieldcommunications module, a global positioning system (GPS) module, amobile communications module, and the like. The wired/wirelesscommunications module included in the communications unit 2010 maytransmit and receive data by being connected to external communicationsnetworks according to various communications standards.

The input unit 2020 may be a module provided for users to controloperations of the electronic device 2000 and may include a mechanicalswitch, a touchscreen, a voice recognition module, and the like. Inaddition, the input unit 2020 may also include a finger mouse device ora mouse operating using a trackball, a laser pointer, or the like. Theinput unit 2020 may further include various sensor modules by whichusers may input data.

The output unit 2030 may output information processed in the electronicdevice 2000 in a form of audio or video, and the memory 2040 may store aprogram, data, or the like, to process and control the processor 2050.The memory 2040 may include one or more semiconductor devices 100, 200,and 300 according to various example embodiments of inventive concepts,and the processor 2050 may store as well as output data by sending acommand to the memory 2040 according to required operations. Theprocessor 2050 may also be implemented by the semiconductor devices 100,200, and 300 according to example embodiments described above.

The memory 2040 may communicate with the processor 2050 through aninterface embedded in the electronic device 2000 or a separateinterface. When the memory 2040 communicates with the processor 2050through a separate interface, the processor 2050 may store or outputdata in or from the memory 2040 through various interface standards,such as SD, SDHC, SDXC, MICRO SD, USB, and the like.

The processor 2050 may control operations of respective units includedin the electronic device 2000. The processor 2050 may perform controland process operations relating to voice calls, video calls, datacommunications, and the like, or may perform control and processoperations to play and manage multimedia. In addition, the processor2050 may process inputs sent by a user through the input unit 2020 andmay output the results through the output unit 2030. Furthermore, theprocessor 2050 may store data required to control operations of theelectronic device 2000 in the memory 2040 or output the data therefrom.

While example embodiments have been shown and described above, it willbe apparent to those skilled in the art that modifications andvariations could be made without departing from the scope as defined bythe appended claims.

What is claimed is:
 1. A semiconductor device, comprising: a substrate;source/drain regions on the substrate, the source/drain regionsextending perpendicular to an upper surface of the substrate; aplurality of nanosheets on the substrate between the source/drainregions, the plurality of nanosheets separated from each other, and theplurality of nanosheets defining channel regions that extend in a firstdirection; a gate electrode on the substrate and surrounding theplurality of nanosheets, the gate electrode extending in a seconddirection intersecting the first direction, the gate electrode includinga length in the first direction that is greater than a space betweenadjacent nanosheets among the plurality of nanosheets; and a gateinsulating layer on the substrate between the plurality of nanosheetsand the gate electrode.
 2. The semiconductor device of claim 1, whereinthe length of the gate electrode in the first direction is greater thanor equal to about 1.2 times the space between the adjacent nanosheets.3. The semiconductor device of claim 1, wherein each of the plurality ofnanosheets includes a length in the range of 30 to 100 nanometers in thefirst direction, each of the plurality of nanosheets includes a width inthe range of 10 to 50 nanometers in the second direction, and each ofthe plurality of nanosheets includes a thickness in the range of 3 to 30nanometers in a third direction perpendicular to the upper surface ofthe substrate.
 4. The semiconductor device of claim 3, wherein the widthof each of the plurality of nanosheets is greater than the thickness ofeach of the plurality of nanosheets, and the width of each of theplurality of nanosheets is less than the length of each of the pluralityof nanosheets.
 5. The semiconductor device of claim 1, wherein a sum ofa thickness of any one of the plurality of nanosheets and the spacebetween the adjacent nanosheets is substantially equal to the length ofthe gate electrode in the first direction.
 6. The semiconductor deviceof claim 1, wherein the gate electrode includes a work function metallayer and a gate metal layer, the work function metal layer is on thegate insulating layer, and the gate metal layer is on the work functionmetal layer.
 7. The semiconductor device of claim 1, wherein the gateinsulating layer includes a first insulating layer and a secondinsulating layer, and a permittivity of the second insulating layer isgreater than a permittivity of the first insulating layer.
 8. Thesemiconductor device of claim 1, wherein the gate electrode includes afirst region and a second region, the first region of the gate electrodeextends between the plurality of nanosheets, the second region of thegate electrode surrounds the first region, and each of the first regionand the second region includes at least one metal layer.
 9. Thesemiconductor device of claim 8, wherein the first region and the secondregion have different stack structures from each other.
 10. Thesemiconductor device of claim 8, wherein a number of metal layersincluded in each of the first and second regions is different from eachother.
 11. The semiconductor device of claim 8, wherein the first regionincludes one metal layer.
 12. The semiconductor device of claim 1,wherein the plurality of nanosheets pass through the gate electrode inthe first direction.
 13. A semiconductor device, comprising: asubstrate; a plurality of nanosheets on the substrate, the plurality ofnanosheets extending in a first direction; and a gate electrode on thesubstrate burying the plurality of nanosheets, the gate electrodeincluding a first region between the plurality of nanosheets and asecond region surrounding the first region, the first region and thesecond region have different stack structures from each other, whereinthe gate electrode includes a plurality of metal layers that are stackedon each other.
 14. The semiconductor device of claim 13, wherein anumber of the metal layers included in the first region is less than anumber of the metal layers included in the second region.
 15. Thesemiconductor device of claim 13, wherein the first region includes onemetal layer.
 16. The semiconductor device of claim 15, wherein the onemetal layer included in the first region is a work function metal layer.17. A semiconductor device, comprising: a pair of source/drain regionsspaced apart from each other in a first direction, the pair ofsource/drain regions including sidewalls that face each other; aplurality of nanosheets between the pair of source/drain regions, theplurality of nanosheets spaced apart from each other along the sidewallsof the pair of source/drain regions, the plurality of nanosheetsincluding a semiconductor material; a gate electrode including a firstregion extending between the plurality of nanosheets and a second regionon an uppermost one of the plurality of nanosheets, the first regionconnected to the second region; and a gate insulating layer between gateelectrode and the plurality of nanosheets, the gate insulating layerextending between the gate electrode and the pair of source/drainregions, wherein a length of the gate electrode in the first directionis greater than a space between adjacent nanosheets among the pluralityof nanosheets, and wherein the gate electrode includes metal layers, anda number of the metal layers included in the first region is less than anumber of the metal layers included in the second region.
 18. Thesemiconductor device of claim 17, wherein the gate insulating layerincludes a first insulating layer and a second insulating layer, and apermittivity of the second insulating layer is greater than apermittivity of the first insulating layer.
 19. The semiconductor deviceof claim 17, further comprising: an spacer that extends between thesidewalls of the pair of source/drain regions and the gate electrode,wherein the spacer extends between the plurality of nanosheets.